1. Field of the Invention
The present invention relates to a method and apparatus of nondestructively measuring impurities, defects and the like in semiconductor wafers, semiconductor chips, and electronic components in a short time period.
2. Description of Related Art
Semiconductor wafers, semiconductor chips and the like have been tested by measuring the amount of impurities, defects or the like contained therein. A method of measuring such impurities contained in semiconductors by an isothermal capacitance transient spectroscopy (ICTS) procedure has been known.
Referring to FIGS. 1 and 2, reference numeral 1 designates a transient capacitance meter system provided with a pulse generator 2, a transient capacitance meter 3, and an A/D converter 4 therewithin. A constant temperature bath 5 is provided with a semiconductor sample 6, and a pair of probes 7 and 8 are connected with the transient capacitance meter 1. The probes 7 and 8 are provided with contact needles 9 and 10, respectively, with pointed ends. Reference numeral 11 designates a computer system, and reference numeral 12 designates a plotter, while reference numeral 13 designates a display screen.
In order to measure impurities contained in the semiconductor sample 6 by the use of the transient capacitance meter system 1, the respective pointed ends of the contact needles 9 and 10 are brought into spaced contact with a portion to be measured of the semiconductor sample 6, at an appointed constant temperature, as shown in FIG. 2. Under such conditions, the semiconductor sample 6 has an appointed magnitude of pulse voltage, generated by the pulse generator 2, applied to it. Subsequently, a signal based on an electrostatic capacitance in the portion to be measured of the semiconductor sample 6 is measured by the transient capacitance meter 3. The signal is subjected to an A/D conversion, followed by being operated upon by a measurement algorithm program in the computer 11, thereby measuring the impurities, defects and the like contained in the semiconductor sample 6.
However, in the conventional isothermal capacitance transient spectroscopy, the ICTS spectrum S(t) has been defined by the following equation, where a capacitance transient waveform, as shown in FIG. 5(A), is expressed by C(t), and S(t) is expressed by the following Equation (1): ##EQU2##
In this case, C.sup.2 (t), which is the square of C(t), is expressed by the following Equation (2): ##EQU3## wherein C.sub.o designates a stationary capacitance and N.sub.p designates a concentration of impurities intentionally added.
A concentration of impurities, N.sub.T, and a thermal emission time constant, .tau., are calculated by the following Equation (3) from a peak intensity S.sub.p of the measured ICTS spectrum and at a peak time t.sub.p : ##EQU4##
However, in the above-described conventional isothermal capacitance transient spectroscopy, when the applied capacitance-change is small as compared with a resolving power of the capacitance meter 3 or external turbulent noises are also generated, then noises are added to the C(t). Thus S(t), which is obtained by directly differentiating the C.sup.2 (t), is violently fluctuated, as shown in FIG. 5(B). As a result, the accuracy of measurement of a specific concentration of impurities, N.sub.T, and the thermal emission time constant, .tau., have been lessened, or impurities of a relatively low concentration will not be able to be detected under such circumstances.
Thus, the prior art is still seeking to provide an improved capacitance testing procedure and apparatus for determining impurities.